Voluntary muscle contraction is controlled by the central nervous system. Voluntary muscle contraction occurs as a result of conscious effort originating in the brain. The brain sends signals, in the form of action potentials, through the nervous system to the motor neuron that innervates several muscle fibers.
Electrical muscle stimulation (EMS), also known as neuromuscular electrical stimulation or electromyostimulation, is the elicitation of muscle contraction using electrical impulses. The impulses are typically generated by a device, and are delivered through electrodes placed on the skin in direct proximity to the muscles to be stimulated. The impulses stimulate motor neurons, causing the muscles to contract. The electrodes are generally gel pads that adhere to the skin. EMS is both a form of electrotherapy and of muscle training.
EMS devices generate electrical impulses that trigger an action potential in muscle nerve fibers (motor neurons). In response to this, the motor neuron produces a response known as a twitch. Twitches performed in succession generated by EMS are the same as a muscle contraction generated by the nervous system in response to regular exercise. The work performed by the muscle fibers varies according to the frequency of the electrical stimulation. For example, 10 impulses per second produces low excitement of fibers, and 120 impulses per second produces high working power in fibers. At the end of contraction muscles relax and return to their original state.
Muscle stimulators use voltage controllers to place a voltage on a stimulator pad affixed to a user's skin to provide a series of pulses at a specific voltage, for a specific period of time, and at a specific frequency, to control rest and contraction of muscles. A pulse width modulation (PWM) scheme may be used to provide outputs to the stimulator pads. However, transitions between a rest phase and a contraction phase, or between a contraction phase and a rest phase, can have, like many electrical signals, an oscillation about the desired voltage when a transition is abrupt. In a muscle stimulator, such oscillation can induce unwanted muscle contraction, or increase discomfort in the user, due to the fluctuations and their effect on muscles.
For reasons such as those stated above, and for other reasons, such as those stated below, which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for, among other things, increased control of the operation of muscle stimulators.